Scanning optical system

ABSTRACT

An optical system is provided for projecting an image of a fixed original onto a moving receiving surface comprising a rotating mirror which combines the two processes of directing a scanning beam of light against the original from a fixed source and directing the image modulated reflected light to a fixed objective lens.

United States Patent Inventor Henry G. Joel New York, N.Y. Appl. No.887,177 Filed Dec. 22, 1969 Patented Aug. 17, 1971 Assignee Ing. C.Olivetti & C.S.p.A.

Ivrea, Italy SCANNING OPTICAL SYSTEM 10 Claims, 2 Drawing Figs.

US. Cl 355/47, 355/49, 355/51, 355/66 Int. Cl G03b 27/50 Field 01'Search 355/8, 47, 49, 51, 60, 66

[56] References Cited UNITED STATES PATENTS 2,234,717 3/1941 Altman etal. 355/49 3,142,224 7/1964 Andrews et al.. 355/47 3,364,816 1/1968Jeffree 355/51 3,451,752 6/1969 Frank 355/66 X 3,481,670 12/1969 Amemiyaet al. 355/66 Primary Examiner-Samuel S. Matthews AssistantExaminer-Richard A. Wintercorn An0meyl(evin McMahon ABSTRACT: An opticalsystem is provided for projecting an image ofa fixed original onto amoving receiving surface comprising a rotating mirror which combines thetwo processes of directing a scanning beam of light against the originalfrom a fixed source and directing the image modulated reflected light toa fixed objective lens.

PATENTED AUBI 7 l9?! SHEET 1 BF 2 Henry G. Joel Afro/nay PATENIED mm (ml3.600.088

sum 2 0F 2 Henry 6. Joel lnven/ar Afro/nay SCANNING OPTICAL SYSTEMBACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to optical systems used in reprographic apparatus forscanning a stationary original and providing a light image on areceiving surface that moves in synchronism with said scanning.

2. Description of the Prior Art I Both for ease and flexibility ofoperation and for safeguarding originals to be reproduced, it isdesirable to maintain originals stationary. With the originalstationary, it is possible to uniformly illuminate the original andprovide an image on a stationary receiving surface. This is called afull-frame exposure and is not too popular due to the extreme difficultyof obtaining uniform illumination over the whole fame at once plus theadded demands on the lens system. Accordingly some form of scanning iscustomary. One such system is disclosed in U.S. Pat. No. 3,43l,05 3 toRichard Wick et al. The Wick et a]. patent uses a scanning mirror andlight source moving at a first speed to scan the original and a pair ofmirrors arranged to intercept the reflected image segment from thescanning mirror and redirect it to a fixed lens. In order to keep theoptical path length constant, .the pair of mirrors is moved in the samedirection as the scanning mirror athalf the speed. This concept is alsodisclosed in U.S. Pat. No. 2,942,538 to Bechtold. The difficulties withthis system are the number of elements that must be moved, the distanceover which they must be moved and the space requirements.

A simpler system using a rotating mirror is disclosed in U.S. Pat. No.2,508,650 to Pratt and Gray. Pratt and Gray place the original so thatits surface is curved and then scan with a rotating plane mirror. Therotating motion provides an angle of reflection for successive imagesegments that is intercepted by a fixed objective lens. (Pratt and Grayinterpose a folded telescoping mirror system in the path to the lens inorder to change magnification.)

A major drawback of Pratt and Gray as well as many similar systems (seealso U.S. Pat. No. 3,221,622 to Aser et al.) is the use of full frameillumination of the original. This has the same difficulties withrespect to attaining uniform illumination as described before plus theadditional inefficiency of illuminating the entire original whileviewing it incrementally through a scanning slit.

SUMMARY OF THE INVENTION According to the present invention an opticalscanning system'is provided in which a single scanning mirror assemblydirects light from a stationary source incrementally across a surface tobe scanned and simultaneously incrementally intercepts the lightreflected from such surface and directs it to a stationary objectivesystem. This system utilizes a single rotating mirror assembly which mayhave very low mass as the only moving part of the optical system. In areprographic apparatus it is well adapted for use with a stationaryoriginal and a copy surface moving in synchronism with the mirrorassembly rotation.

Thus it is an object of the invention to provide an optical scanningsystem for incrementally illuminating and viewing an original with asingle rotatable assembly.

It is a further object of the invention to, define a rotating mirrorscanning system for use with a stationary original and a moving imagingsurface in which the original is illuminated by scanning from a fixedlight source.

Further objects and features of the invention will become apparentuponreading the following description together with the drawing.

, BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of areprographic apparatus using the inventive optical scanning system.

FIG. 2 is a diagrammatic view of a secondembodiment of the inventiveoptical scanning system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 depictselectrophotographic copying apparatus in which stationary original 10 isscanned by single rotating scanning mirror element 11. Mirror element 11scans original 10 with an illuminating beam from light source 12 whichis depicted as linear tube 13, for example a quartz-iodine lamp, backedby reflector 15 which is elliptical with respect to an axisperpendicular to the plane of the drawing. Light source 12 may also be aplurality of point type light sources with reflectors. Positionedadjacent to light source 12 is reflex lens assembly 16 made up of halfthe elements of a objective lens and mirror surface 17 positioned atwhat would be the optical center of a complete objective lens. Lightentering lens assembly 16 passes through the lens elements and isreflected back through them in a double pass to achieve the samefocusing effect as a complete symmetrical objective lens. The paths ofincidence and reflection for this type of lens are'offcenter from andsymmetrical about the optical axis. Original 10 is supported on a curvedtransparent surface such as cylindrical section of glass 18, cylindricalabout rotational axis 20 of mirror- 1!. Lens assembly 16 is positionedto intercept imagemodulated light produced by the scanning beam fromlight source 12 and reflected back against scanning mirror 11. Thisposition of lens assembly 16 is further selected to redirect the lightintercepted by mirror surface 17 to further mirror 21. Mirror surface 22of mirror 21 further reflects the imagemodulated light to aphotosensitive medium in an image plane depicted as sensitizedelectrophotographic paper 23 moving on vacuum platen 25. While notcritical, the mirror surfaces have in each case been depicted as on theilluminated surface of the mirror element, which has the advantage ofavoiding optical path variations due to the refractive index of a glassmirror member.

The axis of rotation 20 of mirror 11 is located at a point tangent tothe mirror (reflective) surface. The size and positioning of the variouselements have to be selected with respect to a series of criticalrequirements. If a one-to-one magnification ratio is desired, as iscommon in reprographic apparatus, the optical path lengthfrom anyscanned segment of original 10 to mirror surface 17 via the surface ofmirror 11 must equal the optical path from mirror surface 17 toelectrophotographic paper 23 via mirror surface 22. The path ofreflected imagemodulated light'from mirror surface 17 to mirror surface22 must clear mirror 11 through all the eflective scanning positions ofmirror 11. This clearance is preferably kept to a minimum in order tokeep the angles of incidence and reflection on mirror 17 small.

In general, the sizes and positions of the various elements must relateto the focal length of the lens assembly which in turn must relate tocost and packaging requirements of specific reprographic apparatus. Itwill be recognized that it is also preferable to choose these parametersso as to minimize the angular rotation of mirror 11, again with the aimof keeping the angles of incidence and reflection at the mirror surfaceas small as possible. For this same reason it is desirable to have lensassembly 16 and light source 12 as close to the proximal scan pathbetween mirror 11 and original 10 as possible while preventing lightfrom light source 12 from directly illuminating any part of original 10or illuminating lens assembly 16 by any reflection other thanimage-modulated reflection from a scanned portion of original 10. Lightbaffling plates (not shown) are positioned to prevent light from source12 directly illuminating mirror 21 or sensitized electrophotographicpaper 23.

The scanning motion of mirror 11 is provided by motor 26 in synchronismwith movement of paper 23 on vacuum platen 25. Vacuum platen 25 isdepicted as comprising plenum chamber 27 evacuated through duct-opening28. Perforated belt 31 is driven by drive roller 30 around plenumchamber 27 and across the top of plenum chamber 27 which is flattenedand perforated to form vacuum platen 25. Drive roller 30 is driven insynchronism with the rotation of mirror 11 so that electrophotographicpaper adhering to belt 31 due to the vacuum is transported throughexposure zone 32 in synchronism with the scanning of original 10.

Paper feed system 33 is depicted as a stack of electrophotographicsheets which can be fed one by one by paper feed member 35. Nip of driverollers 36 follows the-paper-feed member to drive theelectrophotographic sheets through sensitizing station 37, depicted asdual corona charging devices for electrostatically charging a paperbefore it passes to exposure zone 32. Following exposure zone 32 isprocessing station 38 depicted as a liquid electrophotographic processorfrom a carrier 1 in which electroscopic pigmented particles areattracted from a carrier liquid to an electrostatic image. Exposedelectrophotographic sheet 23 is guided by channel 40 into processordrive nip 41 which drives paper 23 through the liquid developer and upinto squeegee nip 42 which transports the copy paper from the processorwhile simultaneously squeegeeing excess carrier liquid from the paper.

Second set of rollers 43 are depicted as heated rollers for fusing theimage and drying the paper as it leaves the copying apparatus.

Since the present invention is directed primarily to the type of opticalsystem employed, the other potions of the reprographic apparatus aredescribed only for purposes of a complete disclosure and may take anydesired form without departing from the invention. For example, theelectrophotographic paper could take the form of some otherlight-sensitive material and could be fed from a roll instead of stackedsheets. The sensitizing station 37 could take any form suitable to thephotosensitive medium employed and the processing station 38 couldutilize dry development techniques.

As depicted in Figure 1, it would be necessary to rotate scanning mirror11 in oscillatory fashion by suitable motion transducing means. However,paper feed system 33 could readily be positioned sufficiently below therotational path of mirror 11 to permit continuous 360 rotation. Specificmechanical means for providing the synchronized rotation are obvious tothose skilled in the art and are not described in detail here.

Figure 2 depicts a more compact embodiment of the inventive opticalsystem arranged so that the illuminating light source illuminates thescanning mirror from substantially the same direction as the position ofthe lens assembly with respect to the scanning mirror. In thisarrangement the same area of the scanning mirror is illuminated both bythe light source ad the reflected image-modulated light, thus requiringa smaller mirror. However, illumination is a little bit less efficientin the specific arrangement illustrated since part of the ellipticalreflector is replaced with a baffle of less desirable shape to preventunmodulated light from reaching the image plane.

As in the embodiment of Figure 1, original 50 is scanned by scanningmirror 51 reflecting a beam of light from light source 52. Light source52 comprises a light bulb 53 backed by a partial elliptical reflector55. Light source 52in this embodiment is positioned laterally adjacentlens assembly 56 and is preferably duplicated on the opposite side oflens assembly 56 to provide more uniform illumination. As in Figure 1,lens assembly 56 is depicted as a reflex lens assembly having areflective mirror surface 57 behind the lens element. To use as small anarea of mirror 51 as possible, bulb 53 can be positioned adjacent mirrorsurface 57 and substantially opposite the optical axis of the lens.

Original 50 is positioned on a window cylindrically curved with respectto rotational axis 60 of mirror 51. It will be noted that in theembodiment of FIG. 2 the axis of rotation of mirror 51 is nearly at oneextreme end of the mirror. Because of this offcenter location of therotational axis, it is preferable in machines using high scanning ratesto add suitable counterbalance to the mirror assembly so as to avoidvibration.

Further mirror 61 is positioned to receive reflection from mirrorsurface 57 of image-modulated light incident thereon from mirror 51.Mirror surface 62 of mirror 61 in turn reflects the image to image plane63, which may be occupied, for example, by a photosensitive member suchas in FIG. 1. The position of light source 52in the embodiment of FIG. 2would allow direct illumination of mirror 61 from a direction that wouldresult in reflection of this direct illumination onto the image plane63. To avoid this, elliptical reflector 55 is interrupted bylight-baffling plate 65 which cuts off the path of direct illuminationto mirror 61. Mirror 51 is driven in oscilla' tory or rotational motionby means of scan drive 66 to scan original 50. FIG. 2 is depicted as isFIG. 1 to provide a one-toone magnification ratio. Image plane 63 forthis purpose is considered to be the bottom surface of glass plate 67.The em bodiment of FIG. 2 is subject to the same general criticalcriteria as set forth for the embodiment of FIG. 1.

While the invention has been described with respect to specificpreferred embodiments, many variations are possible without departingfrom the scope of the invention. For example, instead of using a reflexobjective lens, it is possible to use a conventional symmetricalobjective lens, in which case the image path would continue to the leftas viewed with respect to FIG. 1 and 2 and could then be redirected by astationary mirror to an image plane. This would have the advantage ofreducing some of the light baffling problems. If it is desired to obtaina mirror image such as might be desired for a direct printing plate orfor imaging on a reuseable electrophotographic member from which theimage is to be transferred, mirror 61 can be eliminated or an additionalfurther mirror can be provided.

The present invention can also be used to provide an image on a rotatingdrum by either making the scanning slit narrow enough so that theexposed area of the drum at any instant is essentially flat or byproviding an additional lens such as a field lens to introduce curvatureof the image at the drum surface. While both of the describedembodiments are depicted with one-to-one magnification ratios, themagnification ratio can be readily varied by rearranging the opticalpath lengths in known manner. Such change in magnification would alsorequire suitable modification of the speed of the imaging material orthe imaging member with respect to the rotational speed of the scanningmirror.

Thus the present invention provides a compact optical imaging system forefficient scanning with a single rotating mirror element which may havevery low mass.

I claim:

1. Optical scanning apparatus for incrementally simultaneouslyilluminating and scanning a stationary object and providing an imagecomprising:

a. a light source;

b. means to support an object in an object plane;

c. a scanning mirror positioned to receive light from said source andilluminate a portion of said object plane;

d. an objective lens positioned to intercept light reflected from theilluminated portion o said object plane;

e. means to direct image light from said objective lens to an imageplane; and,

f. means to rotate said mirror so as to incrementally scan said objectplane with light from said source while int rcepting image-modulatedreflected light and redirecting it to said lens.

2. Optical scanning apparatus according to claim 1 in which both saidobjective lens and said light source are fixed.

3. Optical scanning apparatus according to claim 2 in which both saidlight source and said objective lens are positioned in substantially thesame angular position with respect to the direction of the scan.

4. Optical scanning apparatus according to claim 2 in which saidobjective lens is a reflex lens in which the intercepted light isreflected back through the lens elements by a mirror surface inside thelens assembly.

5. Optical scanning apparatus according to claim 4 in which said meansto direct image light comprises a single mirror positioned to receivelight from said lens without reflecting direct light from said sourceupon said image plane.

6. Reprographic apparatus for imaging a stationary original upon amoving photosensitive medium comprising:

a. a scanning mirror having an axis of rotation;

b, means to support an original to be reproduced in a curved planecylindrical about said axis of rotation;

c. a light source positioned to illuminate a portion of said curvedplane by reflection from saidmirror;

.d. an objective lens positioned to intercept light from the illuminatedportion of said curved plane by reflection from said mirror and focus animage of said portion at an image plane;

e. means to move a photosensitive medium through said image plane;

f. means to rotate said mirror about said axis in synchronism with themovement of said photosensitive medium so that successive portions ofsaid curved plane are incrementally illuminated and the image thereoffocused by said lens upon incremental portions of said photosensitivemedium; and, g. means to develop an image on said photosensitive medium.7. Reprographic apparatus according to claim 6 in which said objectivelens is a fixed reflex lens positioned so that it interceptsimage-modulated light from said illuminated portion via said mirror atan angle of incidence offcenter of its optical axis and reflects saidlight back through its lens elements at an angle of reflectionsubstantially symmetrical with said angle of incidence about saidoptical axis.

8. Reprographic apparatus according to claim 6 in which both said lightsource and said objective lens are fixed.

9. Reprographic apparatus according to claim 8 wherein said light sourceis laterally adjacent to said lens.

10. Reprographic apparatus according to claim 8 wherein a further mirrorintercepts image-modulated light from said lens and reflects it uponsaid image plane.

1. Optical scanning apparatus for incrementally simultaneouslyilluminating and scanning a stationary object and providing an imagecomprising: a. a light source; b. means to support an object in anobject plane; c. a scanning mirror positioned to receive light from saidsource and illuminate a portion of said object plane; d. an objectivelens positioned to intercept light reflected from the illuminatedportion of said object plane; e. means to direct image light from saidobjective lens to an image plane; and, f. means to rotate said mirror soas to incrementally scan said object plane with light from said sourcewhile intercepting image-modulated reflected light and redirecting it tosaid lens.
 2. Optical scanning apparatus according to claim 1 in whichboth said objective lens and said light source are fixed.
 3. Opticalscanning apparatus according to claim 2 in which both said light sourceand said objective lens are positioned in substantially the same angularposition with respect to the direction of the scan.
 4. Optical scanningapparatus according to claim 2 in which said objective lens is a reflexlens in which the intercepted light is reflected back through the lenselements by a mirror surface inside the lens assembly.
 5. Opticalscanning apparatus according to claim 4 in which said means to directimage light comprises a single mirror positioned to receive light fromsaid lens without reflecting direct light from said source upon saidimage plane.
 6. Reprographic apparatus for imaging a stationary originalupon a moving photosensitive medium comprising: a. a scanning mirrorhaving an axis of rotation; b. means to support an original to bereproduced in a curved plane cylindrical about said axis of rotation; c.a light source positioned to illuminate a portion of said curved planeby reflection from said mirror; d. an objective lens positioned tointercept light from the illuminated portion of said curved plane byreflection from said mirror and focus an image of said portion at animage plane; e. means to move a photosensitive medium through said imageplane; f. means to rotate said mirror about said axis in synchronismwith the movement of said photosensitive medium so that successiveportions of said curved plane are incrementally illuminated and theimage thereof focused by said lens upon incremental portions of saidphotosensitive medium; and, g. means to develop an image on saidphotosensitive medium.
 7. Reprographic apparatus according to claim 6 inwhich said objective lens is a fixed reflex lens positioned so that itintercepts image-modulated light from said illuminated portion via saidmirror at an angle of incidence offcenter of its optical axis andreflects said light back through its lens elements at an angle ofreflection substantially symmetrical with said angle of incidence aboutsaid optical axis.
 8. Reprographic apparatus according to claim 6 inwhich both said light source and said objective lens are fixed. 9.Reprographic apparatus according to claim 8 wherein said light source islaterally adjacent to said lens.
 10. Reprographic apparatus according toclaim 8 wherein a further mirror intercepts image-modulated light fromsaid lens and reflects it upon said image plane.